Earthbag Architecture: Modern Mud Domes for Sustainable Living
For millennia, humans have built shelters out of the mud beneath their feet. Many modern-day homeowners, particularly those of us who live in the west, might consider the idea of constructing a home out of clay or mud a primitive and anti-hygienic building technique. (Rammed earth construction is seemingly an exception.)
Earthen architecture, however, offers several sustainability and health advantages. Because the primary construction material, raw clay soil, is usually located directly on the building site, earthen architecture has a very low embodied energy footprint. Earthen homes also have high thermal mass. Earthen architecture can incorporate passive solar design to reduce artificial heating and cooling requirements. Earthen houses also protect interior air quality, and when partnered with mineral and earthen plasters, will not emit any VOCs into your home.
In terms of structural strength, earthen architecture is often constructed using techniques that ensure the home lasts for hundreds of years. In the Hadramut region of Yemen, whole cities of earthen skyscrapers (up to nine stories tall) continue to house a growing population.
In the mountains of Guatemala, Kyle and Jolene were looking for an affordable and sustainable way to build a home. They discovered earthbag architecture, otherwise known as the SuperAdobe. They found the idea of making a home almost entirely from materials found on the site of their rural homestead attractive.
"We decided on a SuperAdobe dome because we wanted to learn a new earth-building style, and had great contacts in the area with lots of experience building earthbag structures," they say. "We organized a workshop together and brought friends from all over North America to help and learn.
We wanted to build a unique off-grid tiny home that could be a module in a larger structure later on. The fact that we could put up a dome quickly, without needing to build a roof (the walls are the roof), was a nice factor."
What Are Earthbag Homes?
In southern California, the Iranian-born architect Nader Khalili developed a unique earthen architecture technique called SuperAdobe. The technique was originally designed as a prototype for NASA to create theoretical human settlements on the Moon and Mars. But, Khalili's SuperAdobe later became an affordable and practical housing alternative for refugees, people affected by natural disasters, and the homeless.
Today, tens of thousands of SuperAdobe earthbag homes have built around the world in different climates. This unique earthen building technique offers a pathway to affordable, environmentally friendly, and aesthetically unique dwellings.
What Bags Are Used For Earthbag Homes?
SuperAdobe relies on filling polypropylene bags with soil and sometimes cement aggregate. The method, as developed by Khalili, uses long sandbags filled with slightly damp soil and a 10-to-15 percent Portland cement aggregate. Builders lay the bags in long lines and tamp the bags until firm, a technique similar to that used in rammed earth construction. The builder then places strands of barbed wire between each row of earthbags to prevent slipping. Earthbag homes naturally lend themselves to building unique dome shapes. When covered with a cement-based plaster, these homes require no other roofing material.
One of the unique aspects of earthbag and SuperAdobe homes is the simplicity of construction. Khalili designed the building process to require minimal building materials. According to the California Institute of Earth Architecture which Khalili founded in 1991, the only materials needed to build a SuperAdobe dome are:
- Synthetic, low UV (ultra-violet) resistant degradable sandbags
- Four-point, two-strand, galvanized barbed wire
The construction process is also very DIY-friendly and intentionally simple. SuperAdobe homes, then, can be built by virtually anyone with access to sandbags and a bit of soil.
Why Build Earthbag Homes?
Earthbag homes offer several other advantages and sustainability benefits. Unlike concrete, brick, wood, or other typical home construction materials, earthbag construction requires very little external energy. The reliance on local, raw building materials drastically reduces both the embodied energy and the carbon footprint of the building process. The plastic in the polypropylene bags, the cement aggregate, and the steel barbed wire usually account for no more than five percent of the total building material.
The thick earthen walls act as a thermal mass, allowing the structure to slowly absorb the solar heat during the day and emanate that heat into the home during cooler evenings. This thermal mass can drastically reduce the need for artificial heating and cooling, which accounts for almost 50 percent of the total energy use in modern-day homes.
Earthbag homes are also structurally sound and resilient. When developing this technique, Khalili incorporated modern engineering concepts in structural design, including base-isolation and post-tensioning. The coils made from compressed earth within the polypropylene bags give the walls compressive strength.
Meanwhile, the barbed wire gives the entire structure tensile strength. The earthen nature of the walls provides insulation and natural fire resistance. Earthbag homes have passed several rigorous earthquake code tests in California. The typical dome structure, which is a common option for SuperAdobe construction, is one of the most robust natural geometric structures.
Earthbag homes are usually built with the polypropylene bags commonly used as sandbags during floods. These types of bags are also widely used for feed sacks and can be sourced from recycled sources. The California Institute of Earth Architecture recommends bags specially manufactured as long tubes, which can be cut to the specific length of your wall. The Institute offers affordable SuperAdobe bags that are sold by the roll. A 1,000-yard SuperAdobe roll of polypropylene bag costs $842. If you are having trouble sourcing polypropylene feed sacks or bags, you can also use burlap bags, though these do need to be coated with plaster.
How Do You Keep Earthbags From Rotting?
Earthbag homes, like all earthen architectural techniques, can last for hundreds of years as long as they are protected from rain and water. To achieve the necessary protection:
- For dome-style homes, a thick cement-based plaster is necessary.
- For traditional linear walls, a roof with extended eaves can protect the earthen walls from driving rain.
- Of course, a stem wall made from rock, cinder block, or some other impervious material will also protect earthbags from surface water.
How Long Do Earthbag Homes Last?
When protected from the rain and surface water, earthbag homes can easily last for a lifetime. If the earthbags are not plastered on the exterior, the UV rays from the sun will eventually disintegrate the polypropylene material. However, this can be avoided by merely covering the walls in a cement, earthen, or mineral-based plaster.
Kelly Hart, an expert earthbag builder, believes that earthbag homes will easily last at least a century. The polypropylene bags can even be burned or allowed to disintegrate because they play no role in the overall structural strength of the home.
Building An Earthbag Home
Kyle and Jolene built their SuperAdobe dome home off-the-grid with no electricity and few tools. The bulk of the material was earth dug up from the subsoil on site. "The result is a stable building with a ton of thermal mass, so it holds warmth through the night and is stay a consistently comfortable temperature," they say.
In retrospect, they add, "We would have used less cement for sure, and would probably have built slower and smaller as a result. We rushed into things a bit and had a tight timeframe to get the home finished before the rainy season hit. Knowing our land and microclimate as we do now, we would have gone with a stone foundation for better drainage and added more windows and ventilation. Since initially building, we have gone back to add more windows and installed a rocket mass heater to help with heat and humidity."
Kyle and Jolene say the earthbag or SuperAdobe construction methods "is an awesome and fun way to build, but it has its limitations." For other homeowners wanting to try this method of building, Kyle and Jolene advise, "Plastering the interior spaces can be a challenge. Know your local climate and soil type. Take your time before building to really get to know your site and observe nature's patterns on the land. This will really help you out in the long run and is worth the extra patience."
What States Allow Earthbag Homes?
As with most alternative building techniques, navigating the building codes and laws for earthbag homes can be tricky. Because of the relative "newness" of this building technique, many local building codes will not recognize this earthen building technique. To date, code-approved Super Adobe houses have been built in Hawaii, California, Utah, Arizona, and Kentucky. For homeowners wanting to make an earthbag home in a jurisdiction that doesn't currently allow for this type of construction, getting an engineer's "stamp of approval" can help. Also, educating officials in charge of your building code might be a strategy worth exploring.